How do I select segments of a matrix based on values in a CSV within a loop

I am trying to read in a CSV with integer values and want to select portions of a wav file from which are of interest (a specific time period represented by valuess in y) within a loop. What can I do to make this happen? Example code below:

M = csvread(segments.csv) % 2 columns, 280 rows

for i = 31:3527
    [y,Fs] = audioread(strcat(DirIn,'/',filelist(i).name)); % read in wav file
    z = y([Col 1, Row i+31:Col 2, Row i+31], [1]) % Need help here
    snips_db = 20*log10(z) - Sensitivity - Gain 
    c(end+1;) = snips_db
end

[Jan]

What is the problem with the posted code? What should be different?

A hint: Use fullfile() instead of strcat(), because it is safer.

[Benjamin Colbert]

Firstly,

    z = y([Col 1, Row i+31:Col 2, Row i+31], [1]) % Need help here

Contains no refernece to the matrix M. Second, it seems not very elegant but not suure if there's a better way. I'm a true rookie at coding.

[Star Strider]

An extended description of the problem:

I have a 250 24min wav files. For each file I have a random 30sec period which I want to pull out for analysis. The start times and end times for each 30 sec period is in a CSV.

I want to create a loop that reads in the audiofile, extracts the 30 sec period from the file, analyzes and repears. E.g., Read in file one, downselect file one wav to samples in row one of the CSV. Read in file two, downselct file two to samples in row two of the csv. Etc.

.

[Jan]

@Benjamin Colbert: What is the purpose of "for i = 31:3527"? Where do these limits come from?

If the command to crop the signal does not include a reference to M, insert a reference to M. The readers cannot know the contents of M, so it is your turn either to implement it or to explain the deatails. If we see a not working code, we cannot guess magically its intention:

z = y([Col 1, Row i+31:Col 2, Row i+31], [1]) % Need help here

Which kind of help do you need? What is "Row" and "Col"? Why "+31"? I assume Fs helps to get the indices for specific times.

Answer 1

[Aditya]

Hi Benjamin,

I understand that you want to read segments from a CSV file and use those segments to extract specific time periods from a series of WAV files.

Assuming that your CSV file contains start and end times in seconds for each segment, and you want to extract these segments from the WAV files, here's how you can modify your code:

for i = 31:3527  
    [y, Fs] = audioread(fullfile(DirIn, filelist(i).name)); % read in wav file 
     
    % Extract segments based on the CSV values 
    for j = 1:size(M, 1) % Iterate over each row in the CSV 
        startTime = M(j, 1); % Start time in seconds 
        endTime = M(j, 2); % End time in seconds 
         
        % Convert times to sample indices 
        startSample = round(startTime * Fs) + 1; % Add 1 because MATLAB indices start at 1 
        endSample = round(endTime * Fs); 
         
        % Extract the segment 
        if startSample > 0 && endSample <= length(y) 
            z = y(startSample:endSample, 1); % Assuming you want the first channel 
            snips_db = 20 * log10(abs(z)) - Sensitivity - Gain; 
            c(end+1;) = snips_db;  
        end 
    end 
end 

I've replaced “strcat()” with “fullfile()” for better path handling. Additionally, I've introduced a nested for loop that iterates through the rows of the CSV file to read the start and end times, converting them into sample indices for the WAV file data extraction. This code is a template, and you may adjust it as needed to suit your specific requirements.

Hope this helps!